Synchronous calls may throw an IOException in case of either failing to
parse the REST response in the high-level REST client, the request times out
or similar cases where there is no response coming back from the server.

In cases where the server returns a 4xx or 5xx error code, the high-level
client tries to parse the response body error details instead and then throws
a generic ElasticsearchException and adds the original ResponseException as a
suppressed exception to it.

Executing a DeleteIndexTemplateRequest can also be done in an asynchronous fashion so that
the client can return directly. Users need to specify how the response or
potential failures will be handled by passing the request and a listener to the
asynchronous delete-template method:

The DeleteIndexTemplateRequest to execute and the ActionListener to use when
the execution completes

The asynchronous method does not block and returns immediately. Once it is
completed the ActionListener is called back using the onResponse method
if the execution successfully completed or using the onFailure method if
it failed. Failure scenarios and expected exceptions are the same as in the
synchronous execution case.